1. Field of the Invention
This invention relates to disphragm devices for use in optical instruments such as cameras, and more particularly to a diaphragm device having two or more diaphragm blades arranged across an imaging path of rays in axially displaced relation from each other to define a common exposure aperture of variable size. Still more particularly, it relates to an improvement in structure of the aforesaid diaphragm blades.
2. Description of the Prior Art
At present, most diaphragm devices adapted for use in, for example, motion picture cameras, are of the type having two diaphragm blades, at least one of which is arranged to be movable in linkage with the output shaft of an exposure meter cooperating with an exposure value computing circuit to automatically adjust the size of exposure aperture of the camera. The other diaphragm blade may be fixed stationary, or otherwise movably linked with the first-named diaphragm blade.
In arranging these two diaphragm blades to define a common exposure aperture of which the size is controlled in accordance with the output of the exposure meter accurately and reliably, and also for the purpose of reducing the driven load for the exposure meter itself, in other words, of permitting the employment of an exposure meter having a very small driving torque is controlling movement of the diaphragm blades, it is usual to axially displace the diaphragm blades from each other by a distance sufficiently large to prevent intimate contact therebetween, and therefore production of frictional force therebetween during the aperture-adjusting operation.
This axial separation of these two diaphragm blades gives rise to a problem which becomes serious when the sizes of exposure aperture is decreased to a relatively small value with increase in the level of brightness of a scene being photographed. As a result of such problem, it is impossible to make a uniform exposure of the photographic film as is understandable from the fact that the axial displacement of the diaphragm causes the effective oblique pencile of different angular extent to reach the film.